Anomalous photocurrent transient in polyethylene

Abstract

The photocurrent transient has been measured during the decay period of the dark charging current and during the decay period of the dark discharging current in polyethylene under exciting radiation by a series of rectangular ultraviolet light pulses. The photocurrent depends strongly upon the magnitude of the dark charging current or the dark discharging current, the duration and repetition rate of the light pulses; and it becomes very small when the charging or the discharging current approaches its steady-state value. After the charging current has almost reached its steady-state value, the short-circuited discharging current exhibits anomalous photo-quenching if the electrode previously at the negative polarity during the charging period is illuminated by the light pulses, but this phenomenon does not appear if the electrode previously at the positive polarity during the charging period is illuminated. Analysis of the experimental results indicates that the decay of the dark charging current is associated mainly with the time-dependent trap-filling process due to the electrons injected from the metal-polymer contact, while the decay of the dark discharging current is associated mainly with the time dependent detrapping process. The dominant free carriers generated by exciting radiation are holes. The decay of the photocurrent is attributed to the decrease of the hole lifetime due to the deep hole traps created by the trapped electrons in the acceptor-like electron traps. The photo-quenching phenomenon is interpreted as due to the reduction of the lifetime of the majority electrons thermally released during the discharging period by the photogenerate minority holes.